| Summary: | Understanding how shallow aquifers respond to tropical storms, including the possibility of groundwater contamination via floodwaters that carry pathogens and mobilize contaminants, directly affecting human and ecosystem health, is crucial. Hurricane Hanna made landfall in July 2020, impacting coastal, rural, and urban south Texas with storm surges reaching over 1.2m in Baffin Bay (BB) and floodwaters in the Rio Grande Valley (RGV) over 1m deep. The RGV borders Mexico is densely populated and comprises four counties, several cities, and dozens of towns with encircling lands used for agriculture. A sizable portion of the RGV population lives in impoverished settlements called colonias: lands originally used for agriculture, not bound by municipal regulations, and lacking infrastructure including paved roads, sewage, water connections, and access to portable water. This project aimed to determine aquifer responses to flooding resulting from Hanna via biological and geochemical evaluations over one year. This project also aimed to evaluate the nature of the risk of groundwater contamination in response to other seasonal changes (e.g., times of little to no precipitation or rain lasting weeks and months) in both inland, urban settings and rural, coastal settings. Nutrient levels in groundwater were found to fluctuate based on both hydroclimatic season and time of year. Both dissolved inorganic nitrogen (DIN) and phosphate (HPO4 2- ) were highest during the extended summer storms in 2021, lasting weeks/months, which coincides with the planting season when substantial amounts of fertilizer are used. Most of the samples collected throughout the project had varying amounts of total coliform present in both surface- and groundwater, with the highest concentration in surface water. Most of the groundwater E.coli was below detection limits regardless of the season. However, following Hanna a noticeable E.coli level was measured at one location in RGV, indicating direct contamination of the aquifer from flooding via water ...
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